Automatic meter reading (AMR) systems are generally known in the art. Utility companies, for example, use AMR systems to read and monitor customer meters remotely, typically using radio frequency (RF) communication. AMR systems are favored by utility companies and others who use them because they increase the efficiency and accuracy of collecting readings and managing customer billing. For example, utilizing an AMR system for the monthly reading of residential gas, electric, or water meters eliminates the need for a utility employee to physically enter each residence or business where a meter is located to transcribe a meter reading by hand.
There are several different ways in which current AMR systems are configured, including fixed network and mobile network systems. In a fixed network, such as described in U.S. Pat. No. 5,914,673 to Jennings et al., incorporated by reference herein in its entirety, encoder-receiver-transmitter (ERT)-type endpoint devices at meter locations communicate with readers that collect readings and data using RF communication. There may be multiple fixed intermediate readers located throughout a larger geographic area on utility poles, for example, with each endpoint device associated with a particular reader and each reader in turn communicating with a central system. Other fixed systems can utilize a system including repeaters or relay devices that expand the coverage area for each reader, cell control units (CCUs) that concentrate data and forward the same on to the system head end using a wide area network (WAN) or other suitable communication infrastructure. In simple fixed systems, only one central reader may be utilized with all of the endpoint devices. In a mobile network AMR environment, a handheld, vehicle-mounted, or otherwise mobile reader device with RF communication capabilities is used to collect data from endpoint devices as the mobile reader is moved from place to place.
U.S. Pat. No. 5,918,380 to Schleich et al., incorporated by reference herein in its entirety, discloses a metering system for metering the consumption of electrical energy that includes an ERT-type endpoint device for transmitting a RF signal and a receiver device for receiving the radio frequency signal transmitted by the endpoint device. Time interval consumption messaging is also described, in which a single packet transmission can include data representing multiple meter readings as a function of time. U.S. Pat. No. 4,799,059, incorporated by reference herein in its entirety, discloses an example of a signaling protocol for an ERT packet.
Utility meter endpoints associated with water and gas meters are typically battery-powered, and consequently have a finite amount of energy available for their service life. Because a service life for these endpoints of 10-20 years or more is desirable to reduce the expense of battery replacement, energy conservation is a major design criterion. Packet transmission and reception accounts for a substantial portion of the energy demands for endpoints. Longer and more frequent packet transmissions naturally require more energy.
Even in the case of electrical meter endpoints, which generally have the electrical mains available as a power source, energy conservation related to communications is desirable. For example, during power outages, it would be desirable for electrical meter endpoints to notify the AMR system of their loss of power. One problem associated with providing this outage notification function is the small amount of energy typically stored in the electrical endpoint limits the amount of communication attempts that can be carried out.
A related design criterion for utility meter endpoints is the need for keeping their cost low. Utility providers, which tend to be cost sensitive when making capital expenditures, must still maintain large quantities of endpoints for monitoring utility consumption at each of their many customers. For commercial and industrial customers, multiple endpoints are often needed at certain facilities. When selecting from among competing AMR system suppliers, equipment and infrastructure cost is a major consideration. Energy storage components (such as batteries and large capacitors) are a significant cost item for endpoints, so it is desirable to keep the capacity (and the corresponding cost) of these components to a minimum.
Another important design criterion for new endpoints is the need to support existing AMR infrastructure. Presently, for example, AMR infrastructure exists for reading some 40 million ERT endpoints of the type manufactured by Itron, Inc. of Liberty Lake, Wash. For next-generation utility meter endpoints, recent advances in technologies such as event recognition, increased processing power and data storage capability, and the like, can enable many new and useful features and functionality. For example, modern endpoints can provide time of use (TOU) data, interval consumption data, endpoint status information, telemetry data, and utility supply problem reporting. However, implementing these, and other new features and functions in new endpoints is complicated by the need to overhaul or upgrade the existing AMR infrastructure to support the new endpoint technology.
For instance, many existing fixed and mobile readers that communicate with existing ERTs have limited computing power for detecting various types of packet transmissions. In these receivers, the radio is able to correlate on bit sequences to detect two types of ERT packets, the relatively shorter standard consumption message (SCM) transmitted by mostly older ERT devices, and the interval daily message (IDM) transmitted by the newer endpoint devices in the field. The SCM packets have been used with a fixed length of 96 bits, whereas IDM packets have been used with a fixed length of 92 bytes. Each of these packet types has been used with a rigidly-defined length, structure, and set of field definitions.
While the SCM and IDM message formats are well-suited for many purposes, neither the SCM nor the IDM packet is well-suited for carrying varying types of information. The SCM packet has a very small payload portion, so only very simple information items can be carried in a single SCM packet. By contrast, the IDM packet is quite large, such that the IDM packet format would be inefficient or unwieldy for carrying smaller or medium-length information items.
AMR systems that are currently available are generally one-way, one-and-a-half-way, or two-way systems. In a traditional one-way system, such as the system that uses ubiquitous ERT device, each ERT periodically turns on, or “bubbles up,” to send data to a receiver. One-and-a-half-way describes systems in which a receiver sends a wake-up signal to an endpoint device, which in turn responds by sending utility meter reading data to a receiver. Existing ERT-based AMR systems are either one-way or one-and-one-half-way systems.
Two-way AMR systems are systems in which command and control communications are sent and received between AMR system readers and endpoint devices. One type of AMR system, such as the Water Fixed Network 2.5, or the 433 OMR or 433 Fixed Network manufactured by Itron Inc., supports two-way operation. In this type of system, endpoint devices communicate with fixed or mobile AMR readers, typically, in the 1430 MHz telemetry band using FM modulation. SCM and IDM packets are not used in these non-SCM-based AMR systems. Instead, a different set of consumption and command and control packets, which are most often substantially longer than IDM packets, are used to transport large amounts of consumption data and two-way communications.
Two-way communications have not been widely used in the ERT-based AMR systems. The longer packet formats utilized in the endpoint-based AMR systems are not supported by many existing radios designed for receiving the relatively shorter SCM and IDM packets. Additionally, utilizing multiple different packet types presents a system upgradeability problem for existing ERT-based AMR infrastructure, as existing readers lack the processing power to recognize more than two or three distinct packet types. A practical approach has not yet been proposed for enabling two-way communications in ERT-type AMR systems, and for enabling the use of packet types that are longer than SCM packets but shorter than the existing rpm packets, without major overhaul of the presently-installed legacy devices in the existing ERT-based AMR infrastructure.